No abstract available

[en] The prepulse phenomena in the discharge process of accelerator are analyzed in this paper. The prepulse will result in forming plasma, and further affect the diode performance. To remove or reduce this effect, a crowbar tube with cold cathode was adopted in the accelerator. The results show that prepulse voltage decreased from about 150 kV to 50 kV after adopting crowbar tube. The output power of relativistic backward-wave oscillator increased from 50 MW to 250 MW under the same condition. The frequency of relativistic magnetron tended to be reasonable obviously too

[en] The authors report results from experiments studying X-Band amplification in both cylindrical traveling wave tube (TWT) and coaxial drift tube geometries. In the TWT geometry 800-900 kV, 1-2 kA, 50-100 ns electron beams are injected into cylindrical guides containing slow wave structures. The amplifiers operate in the TM₀₁ mode. With single stage ripple wall slow wave structures gains of order 30 dB have been obtained with output powers of 100 MW. Using a dielectric loaded TWT amplifier gains of 30 dB have also been measured, although at lower output powers of 35 MW. In the coaxial geometry a 9 cm diameter annular, 400 kV, 7 kA, 50 ns electron beam is injected through a 16 cm dielectrically loaded cavity, and an X-Band magnetron provides frequency locking of the interaction. The interaction processes involved in these devices have been studied analytically and also simulated with the MAGIC code. These studies show significant electron energy spreads result from the amplification process in the TWT devices. A magnetic spectrometer has been built to analyze the output energy spectrum of the accelerated electrons. Preliminary results from this experiment show evidence of a change in the electron distribution at the amplifier output when the r.f. power is present

No abstract available

[en] There is a huge interest among the scientific fraternity to generate plasma that can selectively absorb or reflect the incident microwaves. Simulations have been carried out to study the absorption of microwaves in plasma using plane wave as a source. In real experiments, the source of microwaves is not always a plane wave and hence the exact simulated replication of the experiment cannot be done using a plane wave source. In order to generate the exact experimental conditions, a horn antenna has been designed and used as a source. A computer model to study the attenuation of X-band (8-12) microwaves in a plasma medium is prepared and partially validated using suitable initial experiments. The study can be extended to any target microwave frequency band. The present work discusses the preliminary simulations that are carried out to study the effect of plasma frequency (ω_p) and collisional frequency (υ_c) on attenuation of microwaves (MW) of 8-12 GHz using CST®MWS®. The plasma is treated as a Drude dispersive material whose properties are governed by two plasma parameters, namely plasma frequency (ω_p) and collisional frequency (υ_c). The simulation is carried out on an array of plasma tubes enclosed in a housing made of teflon. This chamber is then illuminated with microwaves using a horn antenna unlike other simulations where the source of the signal is a plane wave. Using a horn antenna as the transmitter and receiver allows exact simulation of the experimental conditions in the laboratory. The amount of attenuation is measured by considering the difference in return losses with and without plasma. The attenuation of incident microwave is studied by varying plasma frequency from 0.02 GHz to 3 GHz at a fixed collisional frequency of 10¹⁰ S⁻¹. The simulation is also carried out by varying υ_c from 10⁸ to 10¹¹ S⁻¹ at a constant ωp. An experiment to validate the simulation is designed to validate the simulation results. For experimental purpose, fluorescent tube array (FTA), which is a series connection of commercially available tubes is excited using a high-frequency power supply of suitable voltage. The simulation and initial experimental results are compared and are in good agreement with each other. This model serves as a tool to study the attenuation of MW in plasma with given ω_p and υ_c well before the experiment is carried out. This can also be used to select optimum working points for further experiments. (author)

[en] The SPS accelerating structure is essentially a high energy proton linac, except for a small frequency swing during the acceleration cycle. It is operated almost CW with a travelling wave giving an energy gain around 0.1 MeV/m. The guide-lines for the design of such a structure are explained, and practical solutions are described. (author)

[en] The electron field-emission properties of carbon nanotubes (CNTs) enable the fabrication of new cold cathodes for many X-ray instruments. The utilization of these cathodes is an attractive alternative for thermo-ionic cathodes for generating X-rays. CNT has been successfully incorporated into the x-ray tube. CNT fibers offer some advantages over CNT coating for a new generation of X-ray tube, with low power consumption, long lifetime due to the unraveling effect, and high resolution due to the micro-scale emission area. Further research is needed for CNT fiber for x-ray tube in order to increase the stability and consistency for an application to a portable x-ray machine and high resolution x-ray equipment

[en] A sealing mechanism comprises an elastic packing around a seal cylinder, an outer cylinder slidably fitted into the lower end of the seal cylinder through a spring, a cam cylinder and a claw mounting ring each slidably fitted in the outer cylinder, and a radially rotatable claw mounted to the ring. A glove mechanism has a piston cylinder with a piston rod for locking the sealing mechanism. For mounting the sealing mechanism on a pressure tube, the piston rod is inserted into the cam cylinder and the cylinder is actuated to push the cam cylinder while the sealing mechanism is locked with the glove mechanism. At this place the sealing mechanism is unlocked from the glove, the cam cylinder descends due to its weight to engage the claw with the tube, and the weight of the sealing mechanism is applied through the claw to the tube and to thereby support it, while the packing is elastically deformed by the weight of the sealing mechanism. So long as the sealing mechanism is perfectly installed on the tube, the glove mechanism can not be demounted, and since the initial packing force is automatically increased by the sealing mechanism, the seal is assured by the packing. (Ohno, Y.)

[en] The aim of this study was to obtain a better understanding of delayed hydride cracking (DHC) of Zr-2.5Nb pressure tube with crack growth direction. Curved compact tension (CCT) and cantilever beam (CB) specimens were used to determine the DHC velocity in the longitudinal and radial directions, respectively. DHC test were conducted at 250 .deg. C after charging the specimens with hydrogen to 60 ppm H. The DHC velocity of the Zr-2.5Nb tube depended on the crack growth direction due to the anisotropic characteristic of pressure tube. DHCV in the axial direction was 4 times faster than that in the radial direction and the incubation time for the DHC crack growth in the axial direaction was 5 times faster than that in the radial direaction. This anisotropic DHC behavior of the Zr-2.5Nb tube with crack growth direction was discussed using the nucleation and growth pattern of hydrides on the cracking plane

[en] The CANDU calandria tubes, made of seam welded and annealed Zircaloy-2, have given exemplary service in-reactor. Although not designed as a system pressure containment, calandria tubes may remain intact even in the face of pressure tube rupture. One such incident at Pickering Unit 2 demonstrated the economic advantage of such an outcome, and a case can be made for increasing the probability that other calandria tubes would perform in a similar fashion. Various methods of obtaining stronger calandria tubes are available, and reviewed here. When the tubes are internally pressurized, the weld is the weak section of the tube. Increasing the oxygen concentration in the starting sheet, and thickening the weld, are promising routes to a stronger tube